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Introduction

Digitally Derived Evidence (DDE) is increasingly used in international criminal courts and tribunals to prosecute perpetrators of international crimes. Advanced digital tools, including aerial photography, mobile devices, video, intercepted communications, amongst others, capture new and vast quantities of data, which can add supplementary and supporting data to existing evidence. For example, while an eyewitness account may provide relevant information regarding an event, a satellite image may unearth information that would otherwise be inaccessible. Furthermore, phone and computer records may provide data relevant to an individual's activities, or a video may be geo-located, allowing investigators to explore additional details that a witness may have forgotten.1 Given the proliferation of digitally derived evidence and increasing reliance upon it for prosecutions, there is every possibility that digital evidence may become the primary evidence upon which some convictions are based. The use of DDE raises numerous challenges and legal questions and as such these Guidelines have been created to address the legal lacuna by examining the different evidentiary standards relating to DDE before the international criminal courts and tribunals.

The Leiden Guidelines on the Use of Digitally Derived Evidence in International Criminal Courts and Tribunals (“The Leiden Guidelines”) are intended to assist practitioners by comprehensively outlining the essential elements which should be considered before submitting DDE to an international criminal court or tribunal. The Guidelines are aimed at legal practitioners and have been designed to be practical and easily accessible whilst also being sufficiently detailed and substantiated. A subsidiary goal of the Leiden Guidelines is knowledge management: recognising that DDE represents a developing area of legal practice, the Leiden Guidelines were designed to be flexible enough to accommodate future developments within its existing framework and structure.

A. Definition of DDE

The term ‘Digitally Derived Evidence’ was coined by the DDE Project to encompass both ‘digital evidence,’ which is material that has been “born-digital” in the sense of originating from a “computer environment,” as well as ‘digitized evidence,’ which is analogue material that has been transferred to a digital format.2 The concept is rooted in the following definitions:

International Bar Association (IBA)

'Digital and technologically derived evidence, which means evidence taken from and created by digital devices and via technology, such as cameras, satellites and other 'remote sensing technologies' [...] We distinguish digital evidence, created by digital technology and itself the record or trace of an action or event used for the purpose of proceedings, from the digitization of documents and records for the purpose of storing, organizing and presenting evidence, as for example, with the ICC's E-Court protocol.'3

Human Rights Center, University of California, Berkeley School of Law

'Digital evidence is data that is created, manipulated, stored, or communicated by any device, computer or computer system or transmitted over a communication system, that is relevant to the proceeding.'4

DDE therefore reflects evidence that originates from electronic or digital technology, as well as evidence that would normally fall under another category of evidence but has been copied or preserved by being converted into a digital form.

B. Methodology

The Leiden Guidelines are based on an in-depth analysis of the jurisprudence of the international criminal courts and tribunals. They draw on the findings set out in the DDE Project's extensive Case Summaries, which track the trajectory of digital evidence from its first introduction to its final disposition, providing a deeper understanding of how courts and tribunals have applied their existing evidentiary regimes to digital evidence; as well as the report on Extrapolations from Case Law on the Use of DDE, which extracts key conclusions and findings from the Case Summaries. Practitioners can also consult the KGF's publications Prosecution of International Crimes Using DDE in National Courts, DDE in UN Human Rights Fact-Finding Missions, and DDE in International Criminal Law for further insight. Available online from the Leiden DDE Database, these companion documents provide practitioners with a detailed level of analysis from which they will have the flexibility to expand on points of interest and relevant information. The authors hope these materials will help legal practitioners navigate the evidentiary application of DDE through what is a vast quantity of case law and material.

The focus of the Leiden Guidelines is on the International Criminal Court (ICC)'s practice and guidance, recognising the ICC's position as the permanent international criminal judicial body in comparison with other tribunals (such as the International Criminal Tribunals for the former Yugoslavia and Rwanda (ICTY, ICTR), the International Residual Mechanism for Criminal Tribunals (IRMCT or MICT), the Special Court for Sierra Leone (SCSL), and the Special Tribunal for Lebanon (STL)), which are temporary entities with a more limited mandate. Nevertheless, the Leiden Guidelines recognise that there may be situations where another court or tribunal was required to deal with DDE more extensively. Thus, for some guidelines, those courts other than the ICC were given a more central role in the process of guideline formation. Where appropriate, and with recognition of the fact that practitioners and international courts and tribunals frequently draw from domestic decisions when seeking guidance on novel legal issues, relevant national jurisprudence has been incorporated to provide further depth, detail, and perspective.

C. Structure of the Leiden Guidelines

The Leiden Guidelines address each type of DDE separately in order to take into account their technological and legal particularities. Each section begins with a definition of the DDE category. In so far as is possible, the definitions adopted in the Leiden Guidelines attempt to be reflective of the practice at the international courts and tribunals, even if usage is not always consistent.

Every international court and tribunal has procedural and evidentiary rules, which are comprehensively laid out in a number of documents.5 The Leiden Guidelines seek to supplement these rules, which should always be complied with, by describing their application to the various types of DDE. The Guidelines furthermore complement the ICC’s E-court Protocol, which provides the technical standards by which digital evidence should be prepared and provided to the Court.6

The Leiden Guidelines draw upon the ICC's approach to evidence, as set out by the ICC Trial Chamber in Bemba:

'[F]or an item to be admitted into evidence it must satisfy the three-part test under which it must (i) be relevant to the case; (ii) have probative value; and (iii) be sufficiently relevant and probative as to outweigh any prejudicial effect its admission may cause. Further, [the] determination on the admissibility into evidence of an item has no bearing on the final weight to be afforded to it, which will only be determined by the Chamber at the end of the case when assessing the evidence as a whole.'7

The three limbs of the ICC's approach to evidence are briefly defined below and seek to cover the admissibility issues which might arise. Despite this, application of these principles, even at the ICC, has not been uniform. The Court's approach towards the determination of weight, assessed as a whole, is often difficult to discern. Each Guideline, therefore, offers keywords to help identify the relevant evidentiary principles.

Relevance. Pursuant to Articles 64(9) and 69(4) of the Rome Statute,8 the Court may rule on the relevance of any piece of evidence. Evidence is relevant if it makes the existence of a fact at issue more or less probable.9 It is a relational concept, connecting the evidence in question with the asserted fact sought to be proven or disproven, thus delineating the purpose of the evidence in the trial; this is expressed as the need for evidence to be 'material' to the issue or case.10 The Court has the discretion to exclude evidence it deems irrelevant, although in practice the threshold for exclusion has been high.11

Probative Value. Often used interchangeably with the concept of weight, evidence is probative if it tends to prove or disprove an asserted fact. In other words, evidence that is probative has the quality or function of demonstrating the existence of a fact.12 To be considered probative, evidence must reach a certain threshold. Usually at the admissibility stage, the tendering party only needs to show that the evidence has prima facie probative value.13 An assessment of probative value is based on the indicia of reliability of the evidence, which can relate to the form, content, or origin of the evidence, such as the appearance of documents, corroboration by other evidence already admitted, or the place of discovery.14 One important aspect of reliability is authentication: the tendering party should demonstrate that the evidence is genuine.15

Prejudice. Pursuant to Article 69(4) of the Rome Statute, the Court is to take into account any prejudice that may be caused by evidence to a fair trial or to a fair evaluation of the testimony of a witness.16 The accused's right to a fair and impartial trial is thus protected under this provision.17 However, the Court is only required to take prejudice, potential or actual, into account and does not have to declare the evidence inadmissible.18 The assessment of prejudice is relative, balanced against the probative value of the evidence, collectively affecting the weight the Court should give the evidence.19 This discretion is subject to the mandatory inadmissibility of evidence obtained by means which violate the Rome Statute or internationally recognised human rights if it casts substantial doubt on the reliability of the evidence or whose admission would be antithetical to and would seriously damage the integrity of the proceedings (Article 69(7) of the Rome Statute).20 Certain types of DDE, for example, raise particular concerns about the human right to privacy, as will be discussed in greater detail within the Guidelines.

D. Scope of the Leiden Guidelines

The rules and practice surrounding the use of DDE in international criminal courts and tribunals continue to develop. Digital technology is being used more widely and frequently, not only in the investigation and prosecution of international crimes, but also in their commission. It follows that clearer and more comprehensive discussion of DDE-related considerations is produced as cases proceed to trial. However, this process has not yet occurred in relation to some specific categories of DDE, such that the authors were unable to draw meaningful or authoritative guidelines from the practice of the international criminal courts and tribunals. Accordingly, the Guidelines do not cover the use of social media posts or emails as types of DDE in international criminal proceedings:

Social Media Posts. Social media posts have been used in international criminal proceedings. The ICC Trial Chamber in Bemba et al admitted screenshots of social media profiles,21 while the Defence in Taylor were permitted to show a social media post to a witness22 and had the social media post marked for identification.23 More recently, the Al-Werfalli case is significant in terms of social media evidence,24 as the ICC Pre-Trial Chamber based its findings on, inter alia, social media posts.25 However, none of the Chambers discussed the admissibility of social media evidence or specific evidentiary requirements and as such, no authoritative guidelines could be reasonably deduced or formulated.

Emails. Emails have also been tendered as evidence in international criminal proceedings. The MICT Trial Chamber in Nzabonimpa et al admitted and relied upon emails as evidence of witness interference,26 and the Defence in Taylor presented an email as an item of additional evidence to substantiate the grounds of appeal before the SCSL.27 However, in both cases, the emails were tendered together with other types of evidence. Any discussion of evidentiary issues was not specific to emails, and as such no guidelines could reasonably be deduced or formulated.

There was, nevertheless, sufficient guidance from the international criminal courts and tribunals to formulate Guidelines for the following categories of DDE: (A.) videos, (B.) photographs, (C.) aerial and satellite images, (D.) intercepts, (E.) call data records, and (F.) audio recordings.

  1. International Bar Association, Evidence Matters in ICC Trials (August 2016) 20. ↩

  2. Braga Da Silva, R., Updating the Authentication of Digital Evidence in the International Criminal Court, International Criminal Law Review 1-24 (2021) [2]. ↩

  3. International Bar Association, Evidence Matters in ICC Trials (August 2016) 19. ↩

  4. Alexa Koenig and others, Digital Fingerprints: Using Electronic Evidence to Advance Prosecutions at the International Criminal Court (Human Rights Center, UC Berkeley School of Law 2014) fn 2, citing Stephen Mason, International Electronic Evidence (British Institute of International and Comparative Law 2008). ↩

  5. The Guidelines reference a number of international criminal courts and tribunals:

    ICC: Statute, Rules of Procedure and Evidence, Regulations of the Court, Unified Technical Protocol;

    ICTY: Statute, Rules of Procedure and Evidence, Practice Directions;

    ICTR: Statute, Rules of Procedure and Evidence, Practice Directions;

    IRMCT: Statute, Rules of Procedure and Evidence, Practice Directions;

    SCSL: Statute, Rules of Procedure and Evidence;

    STL: Statute, Rules of Procedure and Evidence. ↩

  6. ICC E-court Protocol ↩

  7. Prosecutor v Bemba (Decision on the admission into evidence of items deferred in the Chamber's "Decision on the Prosecution's Application for Admission of Materials into Evidence Pursuant to Article 64(9) of the Rome Statute" (ICC-01/05-01/08-2299)) ICC-01/05-01/08 (27 June 2013) TC [9]. ↩

  8. cf Rule 89(C) of the ICTY and ICTR Rules of Procedure and Evidence, Rule 105(C) of the IRMCT Rules of Procedure and Evidence, Rule 149(C) of the STL Rules of Procedure and Evidence. ↩

  9. 'Article 69(4)', Commentary on the Law of the International Criminal Court (2017), citing Prosecutor v Katanga and Ngudjolo Chui (Decision on the Bar Table Motion of the Defence of Germain Katanga) ICC-01/04-01/07-3184 (21 October 2011) (TC II) [16]. ↩

  10. Kai Ambos, Treatise on International Criminal Law: International Criminal Procedure, vol 3 (OUP 2016) 457. ↩

  11. Kai Ambos, Treatise on International Criminal Law: International Criminal Procedure, vol 3 (OUP 2016) 457. ↩

  12. Christopher Gosnell, 'Admissibility of Evidence' in Karim A A Khan, Caroline Buisman and Christopher Gosnell (eds), Principles of Evidence in International Criminal Justice (OUP 2010) 385. ↩

  13. Christopher Gosnell, 'Admissibility of Evidence' in Karim A A Khan, Caroline Buisman and Christopher Gosnell (eds), Principles of Evidence in International Criminal Justice (OUP 2010) 385. ↩

  14. Christopher Gosnell, 'Admissibility of Evidence' in Karim A A Khan, Caroline Buisman and Christopher Gosnell (eds), Principles of Evidence in International Criminal Justice (OUP 2010) 386; Nikita Mehandru and Alexa Koenig, 'Open Source Evidence and the International Criminal Court' (Harvard Human Rights Journal, April 2019); Prosecutor v Katanga and Ngudjolo Chui (Decision on the Confirmation of Charges) ICC-01/04-01/07-717 (30 September 2008) (PTC I) [78]. ↩

  15. Christopher Gosnell, 'Admissibility of Evidence' in Karim A A Khan, Caroline Buisman and Christopher Gosnell (eds), Principles of Evidence in International Criminal Justice (OUP 2010) 386. ↩

  16. cf The provisions for the exclusion of evidence whose probative value is substantially outweighed by the need to ensure a fair trial: Rule 89(D) of the ICTY Rules of Procedure and Evidence, Rule 105(D) of the IRMCT Rules of Procedure and Evidence, Rule 149(C) of the STL Rules of Procedure and Evidence. ↩

  17. Christopher Gosnell, 'Admissibility of Evidence' in Karim A A Khan, Caroline Buisman and Christopher Gosnell (eds), Principles of Evidence in International Criminal Justice (OUP 2010) 421. ↩

  18. Christopher Gosnell, 'Admissibility of Evidence' in Karim A A Khan, Caroline Buisman and Christopher Gosnell (eds), Principles of Evidence in International Criminal Justice (OUP 2010) 421. ↩

  19. Wolfgang Schomburg and Jan Christoph Nemitz, 'International Criminal Courts and Tribunals, Procedure', Max Planck Encyclopedias of International Law (February 2019) [25]. ↩

  20. cf The narrower provisions which do not stipulate the norm which must be violated: Rule 95 of the ICTY and ICTR Rules of Procedure and Evidence, Rule 117 of the IRMCT Rules of Procedure and Evidence, Rule 162 of the STL Rules of Procedure and Evidence. ↩

  21. Prosecutor v Bemba et al (Public redacted version of the "Prosecution's Fifth Request for the Admission of Evidence from the Bar Table", 27 November 2015, ICC-01/05-01/13-1498-Conf) ICC-01/05-01/13-1498-Red (30 November 2015) (TC VII) [17]; Prosecutor v Bemba et al (Decision on 'Prosecution's Fifth Request for the Admission of Evidence from the Bar Table') ICC-01/05-01/13-1524 (14 December 2015) (TC VII) [12]. ↩

  22. Prosecutor v Taylor (Transcript) SCSL-03-01-T (9 August 2010) (TC II) 45783, lines 11-12. ↩

  23. Prosecutor v Taylor (Transcript) SCSL-03-01-T (9 August 2010) (TC II) 45795, lines 19-28. ↩

  24. Emma Irving, 'And So It Begins... Social Media Evidence In An ICC Arrest Warrant' (Opinio Juris, 17 August 2017). ↩

  25. Prosecutor v Al-Werfalli (Warrant of Arrest) ICC-01/11-01/17-2 (15 August 2017) (PTC I) [3]. ↩

  26. Prosecutor v Nzabonimpa et al (Judgement) MICT-18-116-T (25 June 2021) (Single Judge) [39]. ↩

  27. Prosecutor v Taylor (Defence motion to present additional evidence pursuant to Rule 115 (Public with public Annexes A-E, G-K and confidential Annex F)) SCSL-03-01-A (30 November 2012) (AC) [8]. The motion was dismissed because the Defence had failed to direct the evidence to a specific finding of fact, as required by Rule 115 of the SCSL Rules of Procedure and Evidence: Prosecutor v Taylor (Decision on Defence motion to present additional evidence pursuant to Rule 115) SCSL-03-01-A (18 January 2013) (AC) [11]. ↩